Question 1207588
<font color=black size=3>
x = number of ten dollar bills
48-x = number of twenty dollar bills


10x = value of all the ten dollar bills 
20(48-x) = value of all the twenty dollar bills


10x+20(48-x) = total value
10x+20(48-x) = 880
10x+960-20x = 880
-10x+960 = 880
-10x = 880-960
-10x = -80
x = -80/(-10)
x = <font color=red>8</font>
48-x = 48-8 = <font color=red>40</font>



Answer:
<font color=red>8</font> ten dollar bills
<font color=red>40</font> twenty dollar bills


Check:
8+40 = 48 bills total
8*10+40*20 = 880 dollars in total value
Both conditions are met to verify the answers above.
</font>